This invention relates to a method for producing a novel aliphatic triisocyanate.
It has long been known that aliphatic isocyanates impart premium properties to urethanes derived therefrom in terms of light stability. However, a conventional aliphatic isocyanate such as hexamethylene diisocyanate is characterized by toxicity which renders its handling and use extremely hazardous.
Accordingly, they are often converted to polyisocyantes having a higher molecular weight before subjecting to a practical use in order to lower the toxicity. Such a conversion may be carried out by reacting a relatively low molecular weight polyisocyanate with various polyfunctional compounds such as polyhydroxyl compounds and biuret derivatives. Examples of those converted polyisocyanates, as derived from hexamethylene diisocyanate, are as follows; ##STR2##
In such a conversion, however, a considerable amount of the starting isocyanates, hexamethylene diisocyanate in the above examples, tends to remain unreacted. As a result the mixtures thus obtained are often still toxic. Such conversion processes also involve a higher production cost. The converted polyisocyanates as mentioned above are usually so viscous that they inevitably require diluents for convenient handling and use, and may be unsuitable for usage as high solid type coatings.
Therefore, it has long been desired to produce polyisocyanates that have a low toxicity and viscosity, and that can give a polyurethane resin or coatings having excellent properties with respect to light stability, water-proof, stabilities against organic and inorganic substances and so on.
It is therefore an object of the present invention to provide a novel aliphatic polyisocyanate especially suitable for preparation of a non-yellowing polyurethane. It is a further object to provide a process to produce the novel polyisocyanate from readily available raw materials in high yield by a simple process.